A two-color serial printer is known, from U.S. Pat. No. 4,430,935, comprising two character wheels, two inking rollers of different colors and two hammers for printing the characters on each of the two wheels on a strip of paper interposed between the hammers and the character wheels. The character wheels, the rollers and the hammers can move synchronously to print one character at a time along a line of printing over the entire width of the paper. By selectively activating one or the other of the hammers, it is possible to print with one or other of two different colors. That printer is very slow since the selected character wheel has to pass successively through all the printing positions in order to print a complete row of characters.
Another printer is also known from the U.S. Pat. No. 4,458,589 in which the characters are disposed in a relief configuration on a rubber mat or sheet which is wrapped around a rotatable drum. A single inking roller rolls against the drum to ink in a single color all the characters which are printed in a serial mode by a line of hammers disposed within the drum the inking roller cannot be easily replaced by a roller of another color, so that the printer cannot print in two colors.